Even though modern computers can easily run Ghost Recon with drastically increased sight lines by removing fog, I find it plays better with fog than without it most of the time.
In all seriousness, it's simple shooting mechanics make long range kind of boring and way too easy with the right weapon. While there are ways to balance it, there is usually some form of serious compromise that has to take place in order to make it work. My favorite maps tend to those with shorter sight lines like jungle maps and those with heavy fog. Urban is interesting, but feels kind of clunky to maneuver through compared to, well...
Earlier tonight on Ice Keep (that castle level from Frostbite) in an 18v18 (mostly AI), I picked off 8 guys with a bolt-action unsuppressed sniper rifle with minimal risk to myself except for when someone got close enough to take out my AI teammates and wound both my legs. My response? I got 2 of those 8 kills by just lying prone and aiming at the guys who got close (this is also with Cloak-and-Dagger v1.4 which has increased stabilization times compared to HU).
OGR is simple and plays best when kept that way. The beautiful thing about shorter sight lines is that it greatly limits how much fancy tech (magnified optics, scopes, etc.) help you. For the most part, it pretty much levels the playing field with all combatants. This forces you to focus more on playing smart. Got a nice sniper rifle? Too bad you can't see that far. Got a suppressor? It's stealth value is limited at shorter ranges. Got your super nice automatic grenade launcher? You need to figure out where your enemy is first in order to make the best use of it.
The game mechanics' simplicity lends itself to relatively shorter ranges where the action is quick and intense (except CQB which I find weaker due to its underdeveloped mechanics even with mods).